GreXXL codexinn please follow our troubleshooting guide and provide additional information to be able to help you.
luceos codexinn clear the cache from the admin area if you can or run php flarum cache:clear from the flarum installation path after changing your url.
luceos codexinn seems apache is throwing an error for some reason. You must have changed something else as well (htaccess perhaps)? Check the troubleshooting guide on how to retrieve error logs for your site: https://docs.flarum.org/troubleshoot
